This invention relates generally to a computer-controlled object-building system and, in particular, to an improved layer manufacturing system for building a three-dimensional object such as a model, molding tool, microelectronic device and micro-electromechanical system (MEMS) using the deposition of fused droplets.
Solid freeform fabrication (SFF) or layer manufacturing is a new rapid prototyping and manufacturing technology. In its most commonly used approach, a SFF system builds an object layer by layer or point by point under the control of a computer. The process begins with creating a Computer Aided Design (CAD) file to represent the geometry of a desired object. This CAD file is converted to a suitable format, e.g. stereo lithography (.STL) format, and further sliced into a large number of thin layers with the contours of each layer being defined by a plurality of line segments connected to form vectors or polylines. The layer data are converted to tool path data normally in terms of computer numerical control (CNC) codes such as G-codes and M-codes. These codes are then utilized to drive a fabrication tool for building an object layer by layer.
The SFF technology has found a broad range of applications such as verifying CAD database, evaluating design feasibility, testing part functionality, assessing aesthetics, checking ergonomics of design, aiding in tool and fixture design, creating conceptual models and sales/marketing tools, generating patterns for investment casting, reducing or eliminating engineering changes in production, and providing small production runs. Although most of the prior-art SFF techniques are capable of making 3-D form models on a macroscopic scale, few are able to directly produce a microelectronic device or micro-electromechanical system (MEMS) that contains micron- or nano-scale functional elements.
In U.S. Pat. No. 4,665,492, issued May 12, 1987, Masters teaches part fabrication by spraying liquid resin droplets, a process commonly referred to as Ballistic Particle Modeling (BPM). The BPM process includes heating a supply of thermoplastic resin to above its melting point and pumping the liquid resin to a nozzle, which ejects small liquid droplets from different directions to deposit on a substrate. Patents related to the BPM technology can also be found in U.S. Pat. No. 5,216,616 (June 1993 to Masters), U.S. Pat. No. 5,555,176 (September 1996, Menhennett, et al.), and U.S. Pat. No. 5,257,657 (November 1993 to Gore). Sanders Prototype, Inc. (Merrimack, N.H.) provides inkjet print-head technology for making plastic or wax models. Multiple-inkjet based rapid prototyping systems for making wax or plastic models are available from 3D Systems, Inc. (Valencia, Calif.). Model making from curable resins using an inkjet print-head is disclosed by Yamane, et al. (U.S. Pat. No. 5,059,266, October 1991 and U.S. Pat. No. 5,140,937, August 1992) and by Helinski (U.S. Pat. No. 5,136,515, August 1992). Inkjet printing involves ejecting fine polymer or wax droplets from a print-head nozzle that is either thermally activated or piezo-electrically activated. The droplet size typically lies between 30 and 100 xcexcm, but could go down to 13 xcexcm. This implies that inkjet printing offers a part accuracy on the order of 13 xcexcm or worse which, for the most part, is not adequate for the fabrication of microelectronic devices.
Methods that involve deposition of metal parts from a steam of liquid metal droplets are disclosed in Orme, et al (U.S. Pat. Nos. 5,171,360; 5,226,948; 5,259,593; 5,340,090) and in Sterett, et al. (U.S. Pat. Nos. 5,617,911; 5,669,433; 5,718,951; 5,746,844). The method of Orme, et al involves directing a stream of a liquid material onto a collector of the shape of the desired product. A time dependent modulated disturbance is applied to the stream to produce a liquid droplet stream with the droplets impinging upon the collector and solidifying into a unitary shape. The method of Sterett, et al entails providing a supply of liquid metal droplets with each droplet being endowed with a positive or negative charge. The steam of liquid droplets is focused by passing these charged droplets through an alignment means, e.g., an electric field, to deposit on a target in a predetermined pattern.
The above-cited prior art droplet deposition methods suffer from the following drawbacks:
(1) Inkjet print-head based systems have been largely limited to ejection and deposition of polymer droplets with very low melting temperature (Tm) or glass transition temperature (Tg) such as wax, high impact polystyrene (HIPS), and acrylonitrile-butadiene-styrene copolymer (ABS). These materials can only be used to make models for form and fit, but not functional parts. Even with these low melting materials, the droplet sizes have been known to be larger than 13 xcexcm (normally 50 xcexcm or larger). When being jetted through an inkjet orifice, the liquid droplets could not go down to a few microns or sub-micron in scale due to the strong viscosity and surface tension effects.
(2) The ejection of metallic or ceramic liquid droplets is expected to be difficult due to the high melting temperatures of these materials. The piezoelectric elements such as lead-zirconate-titanate (PZT) commonly used as an actuator to drive and expel liquid droplets are known to have limited working temperature ranges. They are not particularly suitable for use in a high temperature environment conducive to ejection of metallic or ceramic liquid droplets.
(3) The methods proposed by Orme, et al (e.g., U.S. Pat. No. 5,171,360) and by Sterett, et al. (e.g., U.S. Pat. No. 5,617,911) require a continuous supply of liquid metal droplets. The raw metallic material, normally in bulk quantity in the melt state, has to be maintained in a high temperature for an extended period of time, thereby subject to oxidation. Further, since the supply of liquid droplets is essentially continuous rather than drop-on-demand, it is difficult to prevent droplets from reaching xe2x80x9cnegativexe2x80x9d regions (which are not portions of a cross-section of the object). A mask will have to be used to collect these un-desired droplets. In both cases, the metal droplets arc on the micron scale or larger.
(4) Similarly, in any layer manufacturing method that involves thermal spray (e.g., U.S. Pat. No. 5,301,863), a mask has to be used to screen out undesired droplets.
In U.S. Pat. No. 5,301,863 issued on Apr. 12, 1994, Prinz and Weiss disclose a Shape Deposition Manufacturing (SDM) system. The system contains a material deposition station and a plurality of processing stations (for mask making, heat treating, packaging, complementary material deposition, shot peening, cleaning, shaping, sand-blasting, and inspection). Each processing station performs a separate function such that when the functions are performed in series, a layer of an object is produced and is prepared for the deposition of the next layer. This system requires an article transfer apparatus, a robot arm, to repetitively move the object-supporting platform and any layers formed thereon out of the deposition station into one or more of the processing stations before returning to the deposition station for building the next layer. These additional operations in the processing stations tend to shift the relative position of the object with respect to the object platform. Further, the transfer apparatus may not precisely bring the object to its exact previous position. Hence, the subsequent layer may be deposited on an incorrect spot, thereby compromising part accuracy. The more processing stations that the growing object has to go through, the higher the chances are for the part accuracy to be lost. Such a complex and complicated process necessarily makes the over-all fabrication equipment bulky, heavy, expensive, and difficult to maintain. The equipment also requires attended operation.
The selected laser sintering or SLS technique (e.g., U.S. Pat. No. 4,863,538 issued in September 1989 to Deckard and U.S. Pat. No. 4,944,817 issued July 1990 to Bourell, et al.) involves spreading a full-layer of powder particles and uses a computer-controlled, high-power laser to partially melt these particles at desired spots. Commonly used powders include thermoplastic particles or thermoplastic-coated metal and ceramic particles. The procedures are repeated for subsequent layers, one layer at a time, according to the CAD data of the sliced-part geometry.
In a series of U.S. Patents (U.S. Pat. No. 5,017,317 in May 1991; U.S. Pat. No. 5,135,695 in August 1992; U.S. Pat. No. 5,169,579 in December 1992; U.S. Pat. No. 5,306,447 in April 1994; U.S. Pat. No. 5,611,883 in March 1997), Marcus and co-workers have disclosed a selected area laser deposition (SALD) technique for selectively depositing a layer of material from a gas phase to produce a part composed of a plurality of deposited layers. The SALD apparatus includes a computer controlling and directing a laser beam into a chamber containing the gas phase. The laser causes decomposition of the gas phase and selectively deposits material within the boundaries of the desired cross-sectional regions of the part. A major advantage of this technique is that it is capable of depositing a wide variety of materials to form an object on a layer by layer basis. The prior art SALD technique, however, is subject to the following shortcomings:
(1) Just like most of the prior-art layer manufacturing techniques, the SALD technique is largely limited to producing parts with homogeneous material compositions. Although, in principle, SALD allows for variations in the material composition from layer to layer, these variations can not be easily accomplished with the prior art SALD apparatus. For instance, upon completion of depositing a layer, the remaining gas molecules must be evacuated out of the build chamber, which is then filled with a second gas phase composition. This would be a slow and tedious procedure.
(2) The prior art SALD technique does not readily permit variations in the material composition from spot to spot in a given layer. This is due to the fact that the chamber is filled with a gas phase of an essentially uniform composition during the formation of a specific layer. In other words, the laser beam only decomposes one specific gas composition, leading to the deposition of a uniform-composition layer. In many applications (e.g., xe2x80x9cdirect writingxe2x80x9d or deposition of a microelectronic device) material compositions vary as a function of spatial locations.
(3) The prior art SALD technique has poor resolution, precision or accuracy. The deposition spot size could not be smaller than the laser beam spot size, which is normally quite large. It is difficult to produce micron or sub-micron scale deposition spots with prior art SALD.
In U.S. Pat. No. 4,615,904 issued in October 1986, Ehrlich, et al. disclose a method of growing patterned films on a substrate in a deposition chamber. The method consists of the following steps: (1) pressurizing the chamber with a fluid medium to form a thin absorption layer on the substrate, (2) evacuating the chamber to remove excess fluid medium, (3) pre-nucleating portions of the substrate with a focused energy beam, (4) re-pressurizing the chamber with a fluid medium, and (5) inducing deposition of material from the liquid medium. This method permits growth of a patterned film with deposition occurring primarily on the pre-nucleated portions of the substrate. This method suffers from substantially the same drawbacks as with SALD.
Therefore, an object of the present invention is to provide an improved layer-additive process and apparatus for producing an object with high part accuracy.
Another object of the present invention is to provide a computer-controlled process and apparatus for producing a multi-material 3-D object on a layer-by-layer basis.
Still another object of the present invention is to provide a computer-controlled process and apparatus capable of producing multiple-layer microelectronic devices and other functional parts.
It is another object of this invention to provide a process and apparatus for building a CAD-defined object in which the material composition distribution can be predetermined.
Still another object of this invention is to provide a layer manufacturing technique that places minimal constraint on the range of materials that can be used in the fabrication of a 3-D object.
The Process The objects of the present invention are realized by a process and apparatus for fabricating a three-dimensional (3-D) object on a layer-by-layer basis. In one preferred embodiment, the process comprises positioning a material deposition sub-system a selected distance from a target surface. The material deposition sub-system comprises a multi-channel solid powder delivery device, each channel having a small-sized orifice through which a desired material composition in fine powder form (preferably on a micron, submicron, or nanometer scale) can be dispensed at a predetermined flow rate. The flow of a fine powder from a discharge orifice toward a selected area of the target surface forms a powder travel path. The material deposition sub-system further comprises a focused energy beam, such as a laser beam. The energy beam and the powder travel path intersect each other to form a fusion zone in which a powder is melted-in-flight.
Specifically, a first powder material is dispensed and melted while traveling through a fusion zone. The liquid droplet is directed to strike a first focused area of a target surface and deposit a first volume of material on this first area. The process further comprises operating motion devices so that the target surface is moved relative to the material deposition sub-system in a direction on an X-Y plane defined by first (X-) direction and second (Y-) direction. During this movement operation, a second powder material, of the same or different composition, is dispensed and fused for depositing a second volume of material to a second focused area of the target surface. These procedures are repeated, preferably by using a CAD computer to control the relative movement between the target surface and the material deposition sub-system in selected directions on the X-Y plane, to trace out the cross-section of the first layer of the desired object. The material deposition sub-system is then shifted by a predetermined distance away from the target surface in a Z-direction, perpendicular to the X-Y plane. These X-Y-Z directions form a Cartesian coordinate system. These procedures are then repeated under the control of the CAD computer to deposit consecutive layers in sequence, with each subsequent layer adhering to a preceding layer, thereby forming the desired multiple-layer 3-D object.
Preferably, the above steps are attendant with additional steps of forming multiple layers of an inert material (e.g., an electrically insulating material for a multi-layer microelectronic device) on top of one another to form a support structure for an un-supported feature of an object such as an overhang or isolated island. A support structure may either occupy just a selected area of an individual layer or fully cover the remaining area of a layer otherwise unoccupied by the deposition materials. The deposition materials refer to those materials being fused-in-flight and allowed to deposit on a surface of a previous layer or the target surface. In each layer, the portions of an object occupied by the deposition materials are referred to as the xe2x80x9cpositive regionxe2x80x9d and the remaining unoccupied area is xe2x80x9cnegative regionxe2x80x9d. The support material in the negative region can be deposited by using a separate material-dispensing tool such as an extrusion nozzle, inkjet printhead, or plasma sprayer.
Further preferably, the above cited steps are executed under the control of the CAD computer by taking the following specific procedures: (1) creating a geometry of the 3-D object on a computer with geometry including a plurality of segments defining the object; (2) generating programmed signals corresponding to each of the segments in a predetermined sequence; and (3) moving the deposition sub-system and the target surface relative to each other in response to the programmed signals. To build a multi-material object, each segment is preferably attached with a material composition code that can be converted to programmed signals for activating the deposition of selected material compositions to form a desired material distribution of the finished object. Further preferably, the supporting software programs in the computer comprise means for evaluating the CAD data files of the object to locate any un-supported feature of the object and means for defining a support structure for the un-supported feature. The software is also capable of creating a plurality of segments defining the support structure and generating programmed signals required by a deposition tool to fabricate the support structure.
This deposition tool for dispensing the support structure material may be a separate deposition tool such as an extrusion device, a thermal spray nozzle, or an inkjet print-head. This deposition tool may simply be the deposition sub-system used in building the desired object. In this case, a weaker material, a lower-melting material, or a weaker geometry configuration may be selected for building the support structure. This support structure can then be readily removed upon completion of a given layer or the complete object.
The energy beam power can be adjusted to just partially or completely melt the powder particles while traveling through the fusion zone. Essentially any type of solid powder material that is meltable can be used in this process. In an embodiment, a powder particle is composed of a solid core coated with another material composition that has a lower melting point. This lower melting surface coating more readily allows for partial melting of powder particles and mutual adhesion between particles once deposited.
Another embodiment of this invention is an apparatus comprising a material deposition sub-system, a target surface, motion devices and associated machine controller/indexer, and a computer. The material deposition sub-system is composed of three major components: a multi-channel powder material delivery device, a focused energy beam (a laser beam, e.g.), and optionally a separate dispensing tool for depositing a support structure.
The powder delivery device comprises a multiplicity of flow channels. Each channel has at least two ends, first end being in flow communication with a source of powder particles and second end having a discharge orifice of a predetermined size for dispensing the powder particles. The powder compositions are such that they are readily fused while traveling through the energy beam. The fused droplets readily solidify and adhere to the target surface or a previous layer already deposited on the target surface. The delivery device also comprises valve or switch means located in control relation to these channels for regulating the flow of powder particles through these discharge orifices. The discharge orifices are preferably small in size, being micron or nanometer scaled as desired and consistent with powder particle sizes. Different channels may be supplied with different powder compositions so that one powder material or a mixture of powder material compositions at a time is discharged from selected orifices, fused by the laser beam, and directed to move toward the target surface for depositing a small amount of material on a target spot. This multi-channel arrangement readily allows for variations in the material composition so that the spatial distribution of materials in each layer can be predetermined and well controlled.
In one preferred embodiment, a flow channel may comprise a plurality of chambers separated by dynamic sieves; each sieve being a plate containing holes through which powders of selected sizes can filter through. The sieves are excited to vibrate for preventing agglomeration of particles and for facilitating the migration of fine particles through these holes. Optionally, air may be pumped into a chamber to xe2x80x9cfluidizexe2x80x9d the powder particles, i.e., making these solid particles undergoing constant moving inside the chamber. Preferably, a cascade of two or three chambers are stacked together with first chamber being supplied with powder particles continuously or intermittently. The second chamber, separated from the first by a dynamic sieve, will have fewer particles. The third chamber, separated from the second chamber by a second sieve or valve, is allowed to have a predetermined number of particles at a time. The last of this cascade of chambers is equipped with a particle counting device (e.g., comprising a low-power laser beam and a photo detector) for counting the number of particles inside this chamber. This information is then preferably fed back to a controller for activating the dynamic sieves to replenish the chamber with powder particles. Powder particles may be provided with charges (e.g., negative charges) and the last chamber is provided with an electrode (e.g., positively charged) to direct and/or accelerate the discharge of the powder particles. This chamber assembly makes it possible to provide a few particles (down to a single particle if so desired) at a time through the orifice. This feature now makes it possible to deposit ultra-small domains of selected functional materials in individual layers.
The focused energy beam, preferably comprising a laser beam, is disposed in working proximity to the target surface, creating a small fusion zone proximate the target surface where the powder is melted, partially or completely. The fused droplets are directed to strike the target surface and readily solidify thereon.
The target surface is generally flat and is located in close, working proximity to the discharge orifices of the deposition sub-system to receive discharged powder materials therefrom. The motion devices are coupled to the target surface and the material deposition sub-system for moving the deposition sub-system and the target surface relative to one another in the X-Y plane and in the Z-direction. If necessary, the powder delivery device and the laser beam may be attached together to move congruently or as an integral unit. Preferably, however, this material deposition sub-system, comprising the powder delivery device plus the laser beam, is allowed to remain stationary while the target surface is controlled to move in the X-Y-Z directions. The motion devices are preferably controlled by a computer system for positioning the deposition sub-system with respect to the target surface in accordance with a CAD-generated data file representing the object. Further preferably, the same computer is used to regulate the operations of the material deposition sub-system in such a fashion that materials of predetermined compositions at predetermined proportions are dispensed in predetermined sequences.
The target surface may be provided with a controlled atmosphere wherein the temperature, pressure (including vacuum conditions), and gas composition can be regulated to facilitate deposition and to protect against possible metal oxidation. Preferably, sensor means are provided to periodically measure the dimensions of an object being built and send the acquired dimension data to the CAD computer so that new sets of logical layers may be re-calculated when necessary.
The process and apparatus of this invention have several features, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of this invention as expressed by the claims which follow, its more prominent features will now be discussed briefly. After considering this brief discussion, and particularly after reading the section entitled xe2x80x9cDESCRIPTION OF THE PREFERRED EMBODIMENTSxe2x80x9d one will understand how the features of this invention offer its advantages, which include:
(1) The present invention provides a unique and novel process for producing a three-dimensional object on a layer-by-layer basis under the control of a computer. Due to the small powder size and small size of the energy beam induced fusion zone, this process is amenable to the fabrication of a microelectronic device or micro-electromechanical system (MEMS) device containing micron-, submicron-, and/or nanometer-scale functional elements. In contrast to the large droplets ejected by an inkjet printhead, the size of a liquid droplet produced in the presently invented process is essentially controlled by the particle size of the starting powder material. Fine powder particles on a micron and nanometer scale are readily available.
(2) Most of the prior-art layer manufacturing methods, including selected area laser deposition (SALD) and powder-based techniques such as 3-D printing (3DP) and selective laser sintering (SLS), are largely limited to the fabrication of an object with a uniform material composition. Although the prior art SALD method (e.g., as suggested in U.S. Pat. No. 5,017,317) allows for mixing a plurality of gas phases in a chamber and, thereby, forming a composite material part on a target surface through laser-induced chemical vapor deposition, the material compositions of such a composite part could not be spatially controlled. In contrast, the presently invented process readily allows for the fabrication of an object having a spatially controlled material composition comprising two or more distinct types of material. For example, functionally gradient components can be readily fabricated with the present method.
(3) The presently invented method provides a layer-additive process which places minimal constraint on the variety of materials that can be processed. The powder material compositions may be selected from a broad array of materials.
(4) The present invention makes it possible to directly produce net-shaped functional parts of intended materials (not just models or prototypes), thus eliminating intermediate or secondary processing steps such as final sintering or re-impregnation required of 3DP and SLS. This feature enables this new technology to offer dramatic reductions in the time and cost required to realize functional parts.
(5) The method can be embodied using simple and inexpensive mechanisms, so that the fabricator equipment can be relatively small, light, inexpensive and easy to maintain.